1. Field of Invention
The present invention relates to mobile wireless devices as used in object location systems. In particular, the present invention relates to a method and apparatus for controlling an oscillator frequency in a mobile wireless device.
2. Description of the Background Art
The Federal Communications Commission of the United States promulgated FCC Commercial Mobile Radio Services, 47 C.F.R. §20.18(e) (2001) that requires cellular telephones to be geographically identifiable. As such, cell phone carriers have been developing solutions for identifying the location of cellular telephones.
One solution combines a Global Positioning System (GPS) receiver into a cellular telephone transceiver into an integrated mobile wireless device. The GPS receiver may be a standard receiver such as disclosed in U.S. Pat. No. 4,968,891 (issued Nov. 6, 1990) or an assisted GPS (A-GPS) receiver such as disclosed in U.S. Pat. No. 6,453,237 (issued Sep. 17, 2002).
To simplify the mobile wireless device and reduce manufacturing costs, such an integrated device should use a single component for redundant components in the GPS receiver and the cellular telephone transceiver. One such redundant component is the reference oscillator that is generally located in both the transceiver and the GPS receiver. For example, U.S. Pat. No. 6,122,506 (issued Sep. 19, 2000) discloses such an integrated mobile device comprising a cellular telephone transceiver and a GPS receiver.
In many cellular systems, the oscillator must be adjusted to maintain the RF transmitter frequency within an allowed band. Therefore, there is a need in the art for an integrated mobile device that comprises a single oscillator for use by both the cellular telephone receiver and the GPS receiver and has compensation circuitry that allows the GPS receiver to continue to process signals when the oscillator is adjusted to maintain the cellular transmission frequency.